HIV protease inhibitors (HIV PIs) are used in the highly ctive antiretroviral therapy (HAART). However, HIV PIs are often associated with development of liver damages. The mechanisms of the HIV protease inhibitor- induced liver injury are poorly defined. Emerging evidence indicates that the HIV PIs induce endoplasmic reticulum (ER) stress response which has been shown to play an essential role in liver dysfunction including necroinflammation, hepatic cell death and fatty liver. We previously observed that alcohol consumption, which is a well-recognized co-factor in susceptibility to the infection and progression of HIV, induced hyperhomocysteinemia and ER stress response in the liver. A significant proportion of HIV infected patients abuse alcohol and it is logical to consider that an interplay between the effects of alcohol and HIV PIs contributes to severe hepatic steatosis and injury. We hypothesize that HIV PI and alcohol exert a potentiated effect on ER stress and lipid metabolism which worsens liver injury. We propose to explore the HIV PI-induced ER stress response in both primary mouse and human hepatocytes and to investigate in vivo its interactions with pathogenic effects of alcohol in animals fed alcohol. Our specific aims are: (1) to compare ER stress and hepatic injury induced by single or combined HIV PI treatments in vivo in chronic pair- and alcohol-fed mice, and to assess additive or synergistic effects by examining HIV PI-induced ER stress response in vitro in both primary mouse and human hepatocytes and by monitoring bioavailability of HIV PIs in plasma and culture medium of hepatocytes; (2) to confirm ER stress response in mice fed orally a high methionine low folate diet in the presence or absence of single or combined HIV PIs that mimic the antiretroviral therapy in human; (3) to study synergistic mechanisms of ER stress response by HIV PIs and by alcohol through monitoring calcium releasing into the cytosol in primary mouse and human hepatocytes and through examining proteasome activities and expression and activities of glucose transporters in hepatocytes administered HIV PIs; (4) to isolate non-parenchymal cells (hepatic stellate cells, Kupffer cells, and endothelial cells) and differentiate HIV PI- or alcohol-induced ER stress response in these cell types; (5) to determine in vitro and in vivo the effectiveness of protective molecular chaperones (e.g. 4-phenylbutyrate ) in HIV PI- induced ER stress and liver injury. This project will provide a better understanding of the hepatotoxicity of HIV protease inhibitors and better strategies to improve care for HIV-infected patients.